Deaf children whose hearing losses prevent them from accessing spoken language and whose hearing parents have not exposed them to sign language are effectively deprived of input from a conventional language. Despite their lack of linguistic input, these children develop gesture systems, called homesigns that have many of the properties of natural language. The fact that children can develop certain linguistic properties under relatively impoverished language learning circumstances provides strong evidence for the resilience of these properties. But homesign does not exhibit all of the properties of natural language. The goal of the proposed research is to explore the conditions under which homesign becomes a full-blown language. Deaf children rarely remain homesigners in the US;they either learn a conventional sign language or receive cochlear implants and focus on spoken language. In Nicaragua not only do some homesigners continue to use their gesture systems into adulthood, but 30 years ago large numbers of homesigning children were brought together for the first time and Nicaraguan Sign Language (NSL) was born. NSL has continued to develop as new waves of children enter the community and learn to sign from older peers. The first generation, taken together with subsequent generations and current day homesigners (child and adult), thus provides a living historical record of an emerging language. Although generations of signers and adult homesigners have been studied in Nicaragua, and child homesigners have been studied in other cultures, no one has studied the same linguistic properties across all of these groups, thus limiting the field's ability to determine how each of these varying circumstances contributes to the growth of a linguistic property. The proposed research will chart changes in 3 central aspects of sentence structure (verb structure, argument-specification, and sentence-modulation) across these populations and has 5 aims: (1) To probe the structures child Nicaraguan homesigners use for these 3 functions, and thus explore the contribution children make to linguistic structure. (2) To probe the structures that adult Nicaraguan homesigners use for the 3 functions, and thus explore the impact that cognitive and social maturity has on emerging linguistic structure. (3) To probe the structures that the first cohort of NSL use for the 3 functions, and thus explore the impact that being a receiver, as well as a producer, of a sign system has on the structure of that system. (4) To probe the structures that subsequent cohorts of NSL use for the 3 functions, and thus explore the role that transmission across generations plays in structuring a linguistic system. (5) To probe how hearing speakers in Nicaragua use gesture, with speech and without it, when describing the same situations;gesture may provide the raw materials out of which the deaf individuals in Studies 1-4 forge their sign systems. PUBLIC HEALTH RELEVANCE: The proposed research is designed to identify the capacities that children bring with them to language learning, thereby enabling educators to better help deaf children and hearing children with language disabilities learn a conventional language, be it signed or spoken.